Lens barrel and imaging device

ABSTRACT

An interchangeable lens unit includes a second lens group unit, a focus lens unit, a fourth lens group unit, a zoom ring unit, a focus motor, and a photosensor. The zoom ring unit is arranged to mechanically transmit operational force inputted to a zoom ring to the second lens group unit and the fourth lens group unit. The focus motor is configured to electrically drive the focus lens unit in the Z axis direction with respect to the second lens group unit. The photosensor is configured to detect whether or not the focus lens unit is disposed at a starting point position with respect to the second lens group unit. The starting point position is disposed within the total movement range E of the focus lens unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Applications No. 2008-219215 filed on Aug. 28, 2008. The entire disclosure of Japanese Patent Applications No. 2008-219215 is hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

The technical field relates to a lens barrel with which the focal length can be changed.

2. Description of the Related Art

Conventional digital cameras make use of a zoom lens system with which the focal length can be varied while the object distance of a subject that is in focus (hereinafter also referred to as the subject distance) is kept substantially constant. For example, zoom lens systems are employed in compact digital cameras and digital cameras with interchangeable lenses.

With a conventional lens barrel, for example, as the zoom mechanism operates, the focus lens unit including the focus lens is moved in the optical axis direction by a cam mechanism. This allows the focal length to be varied while the subject distance is kept substantially constant (see, for example, Japanese Laid-Open Patent Application 2006-113289).

A phase difference detection system has been employed as the auto-focus system with conventional interchangeable lens digital cameras.

More recently, however, an interchangeable lens digital camera has been proposed that makes use of a contrast detection system for auto-focusing. With this contrast detection system, for example, the focus lens unit is moved in the optical axis direction while evaluation values at various positions of the focus lens unit are found on the basis of image data. The focus lens unit is moved until the evaluation value goes past its peak, after which the evaluation value is returned to its maximum position to focus the subject image (an optical image of the subject). Thus, in auto-focusing by contrast detection, it is necessary to move the focus lens unit back and forth in the optical axis direction.

Also, since the focus needs to be continued during the capture of moving pictures, the focus lens unit has to be continuously moved back and forth and the peak of the evaluation value detected.

Thus, when a contrast detection system is used, since the focus lens unit is moved in the optical axis direction, making the focus lens unit smaller is preferable when drive speed is taken into account.

However, when a configuration is employed in which the focus lens unit is driven in the optical axis direction by a cam mechanism, as with the lens barrel described in Japanese Laid-Open Patent Application 2006-113289, the focus lens unit ends up being larger or heavier.

In view of this, the inventors of the present application studied a lens barrel with which drive of the zoom mechanism was only performed during manual operation by the user, and drive of the focus lens unit with respect to the zoom mechanism was performed only by an actuator. In this case, because the structure of the focus lens unit and its surrounding components is simplified, the focus lens unit can be smaller.

However, with this lens barrel, since the focus lens is driven by an actuator, if the user operates the zoom mechanism in a state in which no power is supplied to the actuator, there is the possibility of a significant discrepancy in the relationship between the zoom position of the optical system and the position where the focus lens unit is supposed to be. For example, if the focus lens unit needs to be moved to a specific position corresponding to the zoom position, depending on the zoom position of the optical system at the point when the power is turned on, it may take a long time for the focus lens unit to move to the specified position.

Japanese Laid-Open Patent Application 07-199033 discloses a resetting unit for resetting the position of a lens support frame to a specific reference position on the basis of output from a step-out detection unit for detecting step-out of the lens support frame from the actuator, but a constitution that involves reducing start-up time has yet to be proposed.

SUMMARY

It is an object to provide a lens barrel and an imaging device with which start-up time can be reduced.

The lens barrel according to an aspect is a lens barrel for forming an optical image of a subject on an imaging element, comprising a first lens unit, a second lens unit, a focus lens unit, a zoom mechanism, a focus actuator, a starting point detector, and a drive controller. The first lens unit has a first lens element and a first lens support frame that supports the first lens element. The second lens unit has a second lens element arranged to vary the focal length by moving relative to the first lens element in the optical axis direction, and a second lens support frame that supports the second lens element. The focus lens unit has a focus lens arranged to vary the focal state of the optical image by moving relative to the first lens element or the second lens element in the optical axis direction, and a focus lens support frame that supports the focus lens. The zoom mechanism relatively moves the first lens unit and the second lens unit in the optical axis direction, and has a zoom operating unit that is operated by the user. The zoom mechanism mechanically transmits the operating force inputted to the zoom operating unit to at least one of the first lens unit and the second lens unit. The focus actuator is supported by the zoom mechanism to move integrally with the first lens unit, and utilizes electric power to drive the focus lens unit in the optical axis direction with respect to the first lens unit. The starting point detector detects whether or not the focus lens unit is disposed at a starting point position with respect to the first lens unit. The drive controller controls the focus actuator so that the focus lens unit moves within a tracking range including the starting point position.

With this lens barrel, whether or not the focus lens unit is disposed at the starting point position with respect to the first lens unit can be detected by the starting point detector, and furthermore, the starting point position is disposed within the tracking range. The result of this constitution is that the drive time it takes to move the focus lens unit from the starting point position to a specific position within the tracking range can be made shorter. Consequently, the start-up time can be reduced with this lens barrel and an imaging device in which this lens barrel is used.

The term “start-up time” here is the time it takes for the state of the lens barrel to move from a state in which no power is supplied to the focus actuator to a state in which imaging is possible. The start-up time may be, for example, the time from when the power is turned on to the imaging device until imaging is possible, the time until imaging is possible from the point when the operating mode is switched from reproduction mode to imaging mode, or the time until imaging is possible from the release of sleep mode.

The lens barrel here also encompasses an interchangeable lens unit that is used in an interchangeable lens type of imaging device, in addition to a lens barrel that is integrated with a camera body. The imaging device also encompasses an interchangeable lens type of imaging device, in addition to an imaging device in which the camera body and the lens barrel are integrated. Examples of possible imaging devices include digital still cameras, interchangeable lens digital cameras, digital video cameras, portable telephones with a camera function, and PDAs (Personal Digital Assistants) with a camera function. The imaging device encompasses devices capable of capturing only still pictures, devices capable of capturing only moving pictures, and devices capable of capturing still pictures and moving pictures.

The first lens element, the second lens element, and the focus lens may each be made up of a plurality of lenses. Also, a state in which “the focus actuator moves integrally with the first lens unit” encompasses a state in which the focus actuator moves with respect to the first lens unit while moving integrally overall.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure:

FIG. 1 is a simplified diagram of a digital camera;

FIG. 2 is a block diagram of the configuration of a camera body;

FIG. 3 is a simplified oblique view of a digital camera;

FIG. 4A is a top view of a camera body, and FIG. 4B is a rear view of a camera body;

FIG. 5 is a cross section of an interchangeable lens unit (wide angle end);

FIG. 6 is a cross section of an interchangeable lens unit (wide angle end);

FIG. 7 is a cross section of an interchangeable lens unit (telephoto end);

FIG. 8 is a cross section of an interchangeable lens unit (telephoto end);

FIG. 9 is an exploded oblique view of a second lens group unit and a focus lens unit;

FIG. 10 is an exploded oblique view of a second lens group unit and a focus lens unit;

FIG. 11 is a partial oblique view of a focus lens unit;

FIG. 12A is a diagram of the configuration of an optical system (wide angle end), and FIG. 12B is a diagram of the configuration of an optical system (telephoto end);

FIG. 13 is a graph of the relationship between the rotational angle of a zoom ring and the distance of the various members from an imaging sensor;

FIG. 14 is a tracking table for realizing a zoom lens system;

FIG. 15 is a cross section of an interchangeable lens unit (wide angle end);

FIG. 16 is a cross section of an interchangeable lens unit (telephoto end).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

First Embodiment

Summary of Digital Camera

A digital camera 1 will be described through reference to FIGS. 1 to 13. FIG. 1 is a simplified diagram of the digital camera 1. As shown in FIG. 1, the digital camera 1 (an example of the imaging device) is a digital camera with an interchangeable lens, and mainly comprises a camera body 3 and an interchangeable lens unit 2 (an example of the lens barrel) that is removably mounted to the camera body 3. The interchangeable lens unit 2 is mounted via a lens mount 95 to a body mount 4 provided to the front face of the camera body 3.

FIG. 2 is a block diagram of the configuration of the camera body 3. FIG. 3 is a simplified oblique view of the digital camera 1. FIG. 4A is a top view of the camera body 3, and FIG. 4B is a rear view of the camera body 3. FIGS. 5 to 8 are simplified cross sections of the interchangeable lens unit 2. FIGS. 5 and 6 show the state at the wide angle end, and FIGS. 7 and 8 show the state at the telephoto end. FIG. 6 is a cross section in a different plane from that of FIG. 5. FIG. 8 is a cross section in a different plane from that of FIG. 7. FIGS. 9 and 10 are exploded oblique views of a second lens group unit 77 and a focus lens unit 75. FIGS. 12A and 12B are diagrams of the configuration of an optical system L. FIG. 12A shows the state at the wide angle end, and FIG. 12B shows the state at the telephoto end. FIG. 13 is a graph of the relationship between the rotational position of a zoom ring 84 and the distance of the various members from an imaging sensor 11.

In this embodiment, a three-dimensionally perpendicular coordinate system is set with respect to the digital camera 1. The optical axis AZ of the optical system L (discussed below) coincides with the Z axis direction (an example of the optical axis direction). The X axis direction coincides with the horizontal direction when the digital camera 1 is in its portrait orientation, and the Y axis direction coincides with the vertical direction when the digital camera 1 is in its landscape orientation. In the following description, “front” means on the subject side of the digital camera 1 (the Z axis positive direction side), and “rear” means the opposite side from the subject side of the digital camera 1 (the user side, or the Z axis direction negative side).

Interchangeable Lens Unit

The basic configuration of the interchangeable lens unit 2 will be described through reference to FIGS. 1 to 12B. As shown in FIG. 1, the interchangeable lens unit 2 has the optical system L, a lens support mechanism 71 that supports the optical system L, a focus adjusting unit 72, an aperture adjusting unit 73, a blur correction unit 74, and a lens microcomputer 40 (an example of the drive controller).

(1) Optical System

The optical system L is a zoom lens system for forming an optical image of a subject, and is mainly made up of four lens groups. More specifically, as shown in FIGS. 12A and 12B, the optical system L has a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a positive refractive power.

The first lens group G1 has a first lens L1 and a second lens L2 disposed on the imaging sensor 11 side of the first lens L1. The first lens L1 is a negative meniscus lens having a convex face that faces the subject side. The second lens L2 is a positive meniscus lens having a convex face that faces the subject side, and is joined to the first lens L1 via an adhesive layer.

The second lens group G2 has a third lens L3, a fourth lens L4 disposed on the imaging sensor 11 side of the third lens L3, and a fifth lens L5 (an example of the first lens element) disposed on the imaging sensor 11 side of the fourth lens L4. The third lens L3 is a negative meniscus lens having a convex face that faces the subject side. The fourth lens L4 is a biconcave lens. The fifth lens L5 is a biconvex lens.

The third lens group G3 is made up of a sixth lens L6 (an example of the focus lens). The sixth lens L6 is a negative meniscus lens having a convex face that faces the imaging sensor 11 side, and is disposed in the Z axis direction between the fifth lens L5 and a seventh lens L7 (in the Z axis direction between the second lens group G2 and the fourth lens group G4).

The fourth lens group G4 has the seventh lens L7 (an example of the second lens element), an eighth lens L8, a ninth lens L9, a tenth lens L10, an eleventh lens L11, and a twelfth lens L12. The seventh lens L7 is a positive meniscus lens for blur correction, and has a convex face that faces the imaging sensor 11 side. The eighth lens L8 is a biconvex lens. The ninth lens L9 is a biconcave lens, and is joined to the eighth lens L8 via an adhesive layer. The tenth lens L10 is a biconvex lens. The face of the tenth lens L10 on the subject side is aspherical. The eleventh lens L11 is a negative meniscus lens having a convex face that faces the subject side, and is joined to the tenth lens L10 via an adhesive layer. The twelfth lens L12 is a biconvex lens.

As shown in FIGS. 12A, 12B, and 13, when zooming in from the wide angle end to the telephoto end, the first lens group G1 to fourth lens group G4 each move in the Z axis direction along the optical axis AZ toward the subject side. More precisely, when zooming in from the wide angle end to the telephoto end, the space between the first lens group G1 and the second lens group G2 increases, the space between the second lens group G2 and the third lens group G3 increases, and the space between the third lens group G3 and the fourth lens group G4 decreases. An aperture unit 62 (discussed below) moves to the subject side along with the fourth lens group G4.

When focusing from an infinity focal state to a close focal state, the third lens group G3 moves along the optical axis AZ to the subject side.

Furthermore, the seventh lens L7 moves in two directions perpendicular to the optical axis AZ in order to suppress blurring in the optical image attributable to movement of the digital camera 1.

(2) Lens Support Mechanism

The lens support mechanism 71 is for movably supporting the optical system L, and has the lens mount 95, a fixed frame 50, a cam barrel 51, a first holder 52, a first lens group support frame 53, a second lens group support frame 54 (an example of the first lens support frame), a second holder 55 (an example of the first lens support frame), a third lens group support frame 56 (an example of the focus lens support frame), a fourth lens group support frame 61, a zoom ring unit 83 (an example of the zoom mechanism), and a focus ring unit 88.

The lens mount 95 is the portion of the camera body 3 that is mounted to the body mount 4, and has a lens-side contact 91. The fixed frame 50 is a member that rotatably supports the cam barrel 51, and is fixed to the lens mount 95. The fixed frame 50 has a protrusion 50 a at the end on the Z axis direction positive side, three concave portions 50 b provided to the outer periphery, and three linear through-grooves 50 c disposed at an equal pitch around the optical axis AZ. The cam barrel 51 has three convex portions 51 a provided to the inner periphery, three first cam grooves 51 d, three second cam grooves 51 b, and three third cam grooves 51 c. Since the convex portions 51 a of the cam barrel 51 are inserted into the concave portions 50 b of the fixed frame 50, in a state in which relative movement is restricted in the Z axis direction, the cam barrel 51 is supported by the fixed frame 50 to be rotatable with respect to the fixed frame 50.

The first lens group support frame 53 is fixed to the first holder 52 and supports the first lens group G1. The first holder 52 has a longitudinal groove 52 a that is formed on the inner peripheral side and extends in the Z axis direction, and three cam pins 81 that are disposed at a constant pitch around the optical axis AZ. The protrusion 50 a of the fixed frame 50 is inserted in the longitudinal groove 52 a. The cam pins 81 are inserted in the first cam grooves 51 d of the cam barrel 51. This configuration allows the first holder 52 to move in the Z axis direction without rotating with respect to the fixed frame 50. The amount of movement of the first holder 52 with respect to the fixed frame 50 is determined by the shape of the first cam grooves 51 d. Female threads 52 c for attaching a conversion lens and an optical filter, such as a polarizing filter or a protective filter, are formed at the distal end of the first holder 52.

The second lens group support frame 54 is fixed to the second holder 55 and supports the second lens group G2. The second lens group support frame 54 and second holder 55 constitute the second lens group unit 77 (an example of the first lens unit). The second holder 55 has three convex portions 55 b that are disposed at a constant pitch around the optical axis AZ, and three cam pins 82 that are fixed to the convex portions 55 b. The cam pins 82 are inserted into the second cam grooves 51 b. The convex portions 55 b are inserted into the linear through-grooves 50 c of the fixed frame 50. This configuration allows the second lens group support frame 54 and the second holder 55 to move in the Z axis direction without rotating with respect to the fixed frame 50. The amount of movement of the second lens group support frame 54 and the second holder 55 with respect to the fixed frame 50 is determined by the shape of the second cam grooves 51 b.

The third lens group support frame 56 is a member that supports the third lens group G3 (more precisely, the sixth lens L6 that functions as a focus lens), and has a bearing part 56 a, an anti-rotation part 56 b, a rack support 56 c, and a protrusion 56 d. The sixth lens L6 and the third lens group support frame 56 constitute the focus lens unit 75. The second holder 55 supports the front ends of two guide poles 63 a and 63 b that extend in the Z axis direction. A guide pole support plate 65 is a member for supporting the rear end of the guide pole 63 a, and is fixed on the imaging sensor 11 side of the second holder 55. The guide pole 63 a is inserted into the bearing part 56 a, and the guide pole 63 b is inserted into the anti-rotation part 56 b. The third lens group support frame 56 is supported movably in the Z axis direction by the guide poles 63 a and 63 b while being restricted in rotation around the optical axis AZ.

The rack support 56 c is a member that extends from the bearing part 56 a to the Z axis direction negative side, and supports a rack 66 rotatably and movably integrally in the axial direction. The rack 66 has a rack main body 66 a having a plurality of teeth 66 c, and a shaft 66 b that extends in the Z axis direction. The plurality of teeth 66 c mesh with a lead screw 64 a of a focus motor 64. The shaft 66 b is supported by the rack support 56 c, so the rack 66 is able to rotate around the center axis R with respect to the rack support 56 c.

As shown in FIGS. 9 and 11, a torsion coil spring 68 is attached to the rack support 56 c. The torsion coil spring 68 has a wound portion 68 a that generates elastic force, a first end 68 b, and a second end 68 c. The wound portion 68 a is fitted to the shaft 66 b of the rack 66. With the wound portion 68 a twisted, the first end 68 b is hooked onto the rack support 56 c, while the second end 68 c is hooked onto the rack 66. That is, the torsion coil spring 68 imparts rotational force in an A direction to the rack 66, and constantly presses the rack 66 against the lead screw 64 a This reduces backlash between the rack 66 and the lead screw 64 a, and increases the positional accuracy of the focus lens unit 75. Also, since the rack 66 is constantly pressed against the lead screw 64 a, drive force can be more efficiently transmitted from the lead screw 64 a to the rack 66.

The wound portion 68 a of the torsion coil spring 68 is also compressed in the Z axis direction (the direction parallel to the center axis R) between the rack support 56 c and the rack 66. The torsion coil spring 68 imparts a pressing force F to the rack 66, and the torsion coil spring 68 presses the rack 66 against the rack support 56 c. This reduces movement of the rack 66 in the Z axis direction with respect to the rack support 56 c, and further improves the positional accuracy of the focus lens unit 75.

The focus motor 64 (an example of the focus actuator) is fixed to the second holder 55. The focus motor 64 is a stepping motor, for example. The focus motor 64 has the lead screw 64 a as its rotational shaft extending in the Z axis direction. This lead screw 64 a meshes with the rack 66.

The protrusion 56 d is a portion for detecting the starting point of the focus lens unit 75, and is provided at a location that can pass through the detection region of a photosensor 67 (discussed below). In this embodiment, since the third lens group G3 (a focus lens group) is formed by the single sixth lens L6, the weight of the third lens group G3 can be 1 g or less, for example, which allows the drive speed with the focus motor 64 to be higher.

The fourth lens group support frame 61 (an example of the second lens support frame) has a first support frame 57, a second support frame 58, a third support frame 59, and a fourth support frame 60. The fourth lens group G4 and the fourth lens group support frame 61 constitute a fourth lens group unit 78 (an example of the second lens unit).

The first support frame 57 supports the seventh lens L7. The second support frame 58 supports the eighth lens L8 and the ninth lens L9, and also supports the first support frame 57 movably in two directions perpendicular to the optical axis AZ. The second support frame 58 has three cam pins 80 that are disposed at a constant pitch around the optical axis AZ.

The third support frame 59 supports the tenth lens L10 and the eleventh lens L11, and is fixed by screws, for example, to the second support frame 58. The fourth support frame 60 supports the twelfth lens L12, and is fixed by screws, for example, to the third support frame 59. Because of their configuration, the first support frame 57, the second support frame 58, the third support frame 59, and the fourth support frame 60 move integrally along the optical axis AZ.

The first support frame 57 is supported by the second support frame 58 so as to be movable in two directions perpendicular to the optical axis AZ, for example. This configuration allows the first support frame 57 to move integrally in the Z axis direction with respect to the second support frame 58, the third support frame 59, and the fourth support frame 60, while allowing movement in a direction perpendicular to the optical axis AZ.

The zoom ring unit 83 has a ring base 86, the zoom ring 84 (an example of the zoom operating unit), and a linear position sensor 87 that detects the rotational position of the zoom ring 84. The “rotational position of the zoom ring 84” refers to the position of the zoom ring 84 in the rotational direction, and can also be considered to be the rotational angle of the zoom ring 84 from a reference position.

The zoom ring 84 has a cylindrical shape, and is supported by the ring base 86 fixed to the fixed frame 50, so as to be movable around the optical axis AZ in a state in which movement in the Z axis direction is restricted. The zoom ring 84 has a through-hole 84 a at the end on the Z axis direction negative side. A zoom drive pin 85 that is fixed to the cam barrel 51 is inserted into the through-hole 84 a. Consequently, the cam barrel 51 rotates integrally with the zoom ring 84 around the optical axis AZ.

The linear position sensor 87 detects the rotational position and rotational direction in which the user has put the zoom ring 84, and sends the detection result to the lens microcomputer 40. More specifically, the linear position sensor 87 is fixed to the ring base 86 and has a slider 87 a that protrudes outward in the radial direction. This slider 87 a is inserted into a cam groove 84 b formed in the zoom ring 84. When the zoom ring 84 is rotated with respect to the fixed frame 50, the slider 87 a moves in the Z axis direction along the cam groove 84 b. The linear position sensor 87 has a varistor, and when the slider 87 a sliders over a magnetic resistor that is inside this varistor, output (output voltage) that is proportional to the position of the slider 87 a in the Z axis direction can be obtained linearly between terminals at both ends to which a specific voltage has been applied. The output of the linear position sensor 87 is converted into rotational position information, which allows the rotational position of the zoom ring 84 to be detected. The focal length of the optical system L is displayed on the outer peripheral face of the zoom ring 84.

Since the first lens group G1 to fourth lens group G4 are mechanically linked via the lens support mechanism 71, the absolute positions of the first lens group G1 to fourth lens group G4 (such as their positions using a light receiving face 11 a of the imaging sensor 11 as a reference) have a specific relationship to the rotational position of the zoom ring 84. Therefore, if the rotational position of the zoom ring 84 is detected, the absolute positions of the first lens group G1 to fourth lens group G4 with respect to the lens mount 95 can be ascertained. The zoom ring 84 may have another structure instead, such as a movable lever.

The focus ring unit 88 has a focus ring 89 and a focus ring angle detector 90 that detects the rotational angle of the focus ring 89. The focus ring 89 has a cylindrical shape, and is supported by the ring base 86 rotatably around the optical axis AZ in a state in which movement in the Z axis direction is restricted. The rotational angle and rotational position of the focus ring 89 can be detected by the focus ring angle detector 90. The focus ring angle detector 90 has two photosensors (not shown), for example. The focus ring 89 has a plurality of protrusions 89 a that protrude inward in the radial direction and are disposed at equidistant spacing in the rotational direction. Each of these photosensors has a light emitting part (not shown) and a light receiving part (not shown), and the plurality of protrusions 89 a pass in between the light emitting parts and the light receiving parts, allowing the rotational angle and rotational direction of the focus ring 89 to be detected. The focus ring 89 may have another structure instead, such as a movable lever.

(3) Focus Adjusting Unit

The focus adjusting unit 72 has the focus motor 64, a focus drive controller 41, and the photosensor 67 (an example of the position sensor). The focus motor 64 is fixed to the second holder 55 and drives the focus lens unit 75 in the Z axis direction with respect to the second lens group unit 77. The drive of the focus lens unit 75 with respect to the second lens group unit 77 is performed by the focus motor 64 alone. In other words, in a state in which the focus motor 64 is not driving the focus lens unit 75 (such as when no power is being supplied to the focus motor 64), the focus lens unit 75 cannot be moved with respect to the second lens group unit 77. In this case, the focus lens unit 75 moves in the Z axis direction integrally with the second holder 55.

The lead screw 64 a of the focus motor 64 rotates on the basis of a drive signal inputted from the focus drive controller 41. The rotary motion generated by the focus motor 64 is converted by the lead screw 64 a and the rack 66 into linear motion of the focus lens unit 75 in the Z axis direction. Consequently, the focus lens unit 75 can move in the Z axis direction with respect to the second lens group unit 77.

With this digital camera 1, to achieve a zoom lens system with which the focal length can be varied while keeping the subject distance substantially constant, the focus lens unit 75 is driven by the focus adjusting unit 72 on the basis of a tracking table stored ahead of time in the lens microcomputer 40. This type of tracking is called electronic tracking here.

The tracking table contains information indicating the position of the focus lens unit 75 where the focused subject distance remains substantially constant even if the focal length changes (more precisely, the position of the focus lens unit 75 with respect to the second lens group unit 77). The phrase “the subject distance remains substantially constant” means that the amount of change in the subject distance falls within a specific subject field depth. Electronic tracking will be discussed below.

Referring to FIG. 9, the photosensor 67, which detects the starting point position of the focus lens unit 75, is installed in the second holder 55. This photosensor 67 has a light emitting part (not shown) and a light receiving part (not shown). When the protrusion 56 d of the third lens group support frame 56 passes between the light emitting part and the light receiving part, the photosensor 67 can detect the presence of the protrusion 56 d. That is, the starting point position of the focus lens unit 75 with respect to the second lens group unit 77 can be detected by the photosensor 67. In other words, the photosensor 67 is a starting point detector that detects the starting point position of the third lens group G3 with respect to the second lens group G2. The lens microcomputer 40 drives the third lens group G3 to the starting point position, and checks whether the focus lens unit 75 (the third lens group G3) is in the starting point position by using a signal from the photosensor 67.

The starting point position that can be detected by the photosensor 67 is an absolute position that never moves with respect to the second lens group unit 77. Accordingly, when the position of the focus lens unit 75 is reset to the starting point position with respect to the second lens group unit 77, the photosensor 67 drives the focus lens unit 75 to the position where the protrusion 56 d for starting point detection is detected. When the power switch 25 is turned off, the focus lens unit 75 is driven by the focus motor 64 to a position where the protrusion 56 d of the third lens group 56 is detected by the photosensor 67 regardless of the position of focus lens unit 75, for example. Upon completion of the drive of the focus lens unit 75, the power supply to the digital camera 1 is halted. Conversely, when a power switch 25 of the digital camera 1 is turned on, the focus motor 64 drives the focus lens unit 75 to a specific position determined on the basis of the tracking table. The starting point detector is not limited to being a photosensor, and may instead be a combination of a magnet and a magnetic sensor, for example.

(4) Aperture Adjusting Unit

The aperture adjusting unit 73 has the aperture unit 62 fixed to the second support frame 58, an aperture drive motor (not shown) that drives the aperture unit 62, and an aperture drive controller 42 that controls the aperture drive motor. The aperture drive motor is a stepping motor, for example. The aperture drive motor is driven on the basis of a drive signal inputted from the aperture drive controller 42. The drive force generated by the aperture drive motor drives aperture blades 62 a in the opening and closing directions. The aperture value of the optical system L can be changed by driving the aperture blades 62 a.

(5) Blur Correction Unit

The blur correction unit 74 is for reducing blurring of the optical image attributable to movement of the interchangeable lens unit 2 and the camera body 3, and has an electromagnetic actuator 46, a position detecting sensor 47, and a blur correction microcomputer 48.

The electromagnetic actuator 46 drives the first support frame 57 in a direction perpendicular to the optical axis AZ. More specifically, the electromagnetic actuator 46 has a magnet (not shown) and a coil (not shown), for example. For instance, the coil is provided to the first support frame 57, and the magnet is fixed to the second support frame 58.

The position detecting sensor 47 is for detecting the position of the first support frame 57 with respect to the second support frame 58, and is a hole element, for example. A movement detecting sensor (not shown) such as a gyro sensor is installed in the interchangeable lens unit 2. The blur correction microcomputer 48 controls the electromagnetic actuator 46 on the basis of the detection result of the position detecting sensor 47 and the detection result of the movement detecting sensor. Consequently, blurring of the optical image attributable to movement of the digital camera 1 can be reduced.

Reducing blurring of the subject image may instead be accomplished by electronic blur correction, in which blurring that appears in an image is corrected on the basis of image data outputted from the imaging sensor 11. Also, blurring of the subject image may be reduced by a sensor shift method in which the imaging sensor 11 is driven in two directions perpendicular to the optical axis AZ.

(6) Lens Microcomputer

The lens microcomputer 40 has a CPU (not shown), a ROM (not shown), and a memory 40 a, and various functions can be performed by reading programs stored in the ROM into the CPU. For instance, the lens microcomputer 40 can check whether the focus lens unit 75 is in the starting point position by using a detection signal from the photosensor 67.

The memory 40 a is a nonvolatile memory, and can hold stored information even when no power is being supplied. The memory 40 a contains a tracking table (discussed below) for realizing a zoom lens system, or information related to the interchangeable lens unit 2 (lens information), for example. The lens microcomputer 40 controls the focus motor 64, and the focus lens unit 75 is driven by the focus motor 64 in the Z axis direction, on the basis of this tracking table. An operation in which the position of the focus lens unit 75 is made to conform to changes in the focal length on the basis of a tracking table will hereinafter be referred to as electronic tracking.

The lens microcomputer 40 has a counter 40 b for counting the number of pulses of the focus motor 64. The counter 40 b is set to a count of “+1” when the focus lens unit 75 is driven to the Z axis direction positive side, and to a count of “−1” when the focus lens unit 75 is driven to the Z axis direction negative side. The lens microcomputer 40 can ascertain the relative position of the third lens group G3 with respect to the second lens group G2 (the position of the focus lens unit 75 with respect to the second lens group unit 77) by thus counting the number of drive pulses of the focus motor 64.

For example, the rack 66 is driven by 0.6 mm in the Z axis direction for every rotation of the lead screw 64 a of the focus motor 64. If the focus motor 64, which has a 10-pole magnet, is driven by 1-2 phase excitation, then the rack 66 is driven in the Z axis direction by 0.6/20/2=0.015 mm (15 μm) per pulse. During micro-step drive, the rack 66 can be driven in even finer units. Using a stepping motor allows the focus lens unit 75 to be driven in fine units, and reduces backlash during reverse drive, for example. That is, selecting a stepping motor as the focus motor 64 affords very precise focus adjustment. Also, counting the number of drive pulses allows the current position of the focus lens unit 75 with respect to the second lens group unit 77 to be ascertained, and allows the amount of drive of the focus lens unit 75 to be calculated.

Camera Body

The basic configuration of the camera body 3 will be described through reference to FIGS. 1 to 4B. As shown in FIGS. 1 to 4B, the camera body 3 has a case 3 a, a body mount 4, an operating unit 39, an image acquisition unit 35, an image display unit 36, a viewfinder unit 38, a body microcomputer 10 (an example of the drive controller, and an example of the auxiliary operation detector), and a battery 22 (an example of the main power supply).

(1) Case

The case 3 a constitutes the outer part of the camera body 3. As shown in FIGS. 4A and 4B, the body mount 4 is provided to the front face of the case 3 a, and the operating unit 39 is provided to the rear and top faces of the case 3 a. More specifically, a display unit 20, the power switch 25, a mode selector dial 26, a navigation key 27, a menu setting button 28, a setting button 29, a mode selector button 34, and a moving picture capture operation button 24 are provided to the rear face of the case 3 a. A shutter button 30 is provided to the top face of the case 3 a.

(2) Body Mount

The body mount 4 is the portion of the interchangeable lens unit 2 where the lens mount 95 is mounted, and has a body-side contact (not shown) that can be electrically connected with the lens-side contact 91. The camera body 3 is able to send and receive data to and from the interchangeable lens unit 2 via the body mount 4 and the lens mount 95. For example, the body microcomputer 10 (discussed below) sends the lens microcomputer 40 a control signal, such as an exposure synchronization signal, via the body mount 4 and the lens mount 95.

(3) Control Unit

As shown in FIGS. 4A and 4B, the operating unit 39 has various controls that the user can use to input operating information. For instance, the power switch 25 is a switch for turning the power on and off to the digital camera 1 or the camera body 3. When the power is turned on with the power switch 25, power is supplied to the various parts of the camera body 3 and the interchangeable lens unit 2.

The mode selector dial 26 is used to switch the operating mode, such as still picture capture mode, moving picture capture mode, or reproduction mode, and the user can turn the mode selector dial 26 to switch the operating mode. When the still picture capture mode is selected with the mode selector dial 26, the operating mode is switched to the still picture capture mode, and when the moving picture capture mode is selected with the mode selector dial 26, the operating mode is switched to the moving picture capture mode. In the moving picture capture mode, basically moving picture capture is possible. When the reproduction mode is selected with the mode selector dial 26, the operating mode is switched to the reproduction mode, allowing the captured image to be displayed on the display unit 20.

The navigation key 27 is used to select the left, right, up, and down directions. The user can use the navigation key 27 to select the desired menu from various menu screens displayed on the display unit 20, for example.

The menu setting button 28 is for setting the various operations of the digital camera 1. The setting button 29 is for executing the operations of the various menus.

The moving picture capture operation button 24 is for starting and stopping the capture of moving pictures. Even if the operating mode selected with the mode selector dial 26 is the still picture capture mode or the reproduction mode, when the moving picture capture operation button 24 is pressed, the operating mode is forcibly changed to the moving picture capture mode, and moving picture capture begins, regardless of the setting on the mode selector dial 26. When this moving picture capture operation button 24 is pressed during the capture of a moving picture, the moving picture capture ends and the operating mode changes to the one selected on the mode selector dial 26, that is, to the one prior to the start of moving picture capture. For example, if the still picture capture mode has been selected with the mode selector dial 26 when the moving picture capture operation button 24 is pressed, the operating mode automatically changes to the still picture capture mode after the moving picture capture operation button 24 is pressed again.

The shutter button 30 is pressed by the user to capture an image. When the shutter button 30 is pressed, a timing signal is outputted to the body microcomputer 10. The shutter button 30 is a two-stage switch that can be pressed half way down or all the way down. Light measurement and ranging are commenced when the user presses the button half way down. When the user presses the shutter button 30 all the way down in a state in which the shutter button 30 has been pressed half way down, a timing signal is outputted, and image data is acquired by the image acquisition unit 35.

The macro imaging switch button 23 is used to switch between normal imaging and macro imaging. For instance, when the user presses the macro imaging switch button 23, a tracking table corresponding to 0.3 m, which is the minimum subject distance, is automatically selected by the lens microcomputer 40.

As shown in FIG. 1, a lens attachment button 99 (an example of the lens attachment operating unit) for attaching and removing the interchangeable lens unit 2 to and from the camera body 3 is provided to the front face of the camera body 3. The lens attachment button 99 has a contact (not shown) that is in its “on” state when the button is pressed by the user, for example, and is electrically connected to the body microcomputer 10. When the lens attachment button 99 is pressed, the built-in contact is switched on, and the body microcomputer 10 recognizes that the lens attachment button 99 has been pressed.

(4) Image Acquisition Unit

The image acquisition unit 35 mainly comprises the imaging sensor 11 (an example of the imaging element) such as a CCD (Charge Coupled Device) that performs opto-electrical conversion, a shutter unit 33 that adjusts the exposure state of the imaging sensor 11, a shutter controller 31 that controls the drive of the shutter unit 33 on the basis of a control signal from the body microcomputer 10, and an imaging sensor drive controller 12 that controls the operation of the imaging sensor 11.

The imaging sensor 11 is a CCD (Charge Coupled Device) sensor, for example, that converts the optical image formed by the optical system L into an electrical signal. The imaging sensor 11 is driven and controlled on the basis of timing signals generated by the imaging sensor drive controller 12. The imaging sensor 11 may instead be a CMOS (Complementary Metal Oxide Semiconductor) sensor.

The shutter controller 31 drives a shutter drive actuator 32 and operates the shutter unit 33 according to a control signal outputted from the body microcomputer 10 that has received a timing signal.

The auto-focusing method that is employed in this embodiment is a contrast detection method that makes use of image data produced by the imaging sensor 11. Using a contrast detection method allows high-precision focal adjustment.

(5) Body Microcomputer

The body microcomputer 10 is a control device that is the command center of the camera body 3, and controls the various components of the digital camera 1 according to operation information inputted to the operation unit 39. More specifically, the body microcomputer 10 is equipped with a CPU, ROM, and RAM, and the programs held in the ROM are read by the CPU, allowing the body microcomputer 10 to perform a variety of functions. For instance, the body microcomputer 10 has the function of detecting that the interchangeable lens unit 2 has been mounted to the camera body 3, or the function of acquiring information about controlling the digital camera 1, such as information about the focal length from the interchangeable lens unit 2.

The body microcomputer 10 is able to receive signals from the power switch 25, the shutter button 30, the mode selector dial 26, the navigation key 27, the menu setting button 28, and the setting button 29. Various information related to the camera body 3 is held in a memory 10 a inside the body microcomputer 10. The memory 10 a is a nonvolatile memory, and can hold stored information even when no power is being supplied.

Also, the body microcomputer 10 periodically produces a vertical synchronization signal, and produces an exposure synchronization signal on the basis of the vertical synchronization signal in parallel with the production of the vertical synchronization signal. The body microcomputer 10 can produce an exposure synchronization signal, since the body microcomputer 10 ascertains beforehand the exposure start timing and the exposure stop timing based on the vertical synchronization signal. The body microcomputer 10 outputs a vertical synchronization signal to a timing generator (not shown), and outputs an exposure synchronization signal at a specific period to the lens microcomputer 40 via the body mount 4 and the lens mount 95. The lens microcomputer 40 acquires position information about the focus lens unit 75.

The imaging sensor drive controller 12 produces an electronic shutter drive signal and a read signal of the imaging sensor 11 at a specific period on the basis of the vertical synchronization signal. The imaging sensor drive controller 12 drives the imaging sensor 11 on the basis of the electronic shutter drive signal and the read signal. That is, the imaging sensor 11 reads to a vertical transfer part (not shown) the image data produced by numerous opto-electrical conversion element (not shown) present in the imaging sensor 11, according to the read signal.

The body microcomputer 10 also controls the focus adjusting unit 72 (discussed below) via the lens microcomputer 40.

The image signal outputted from the imaging sensor 11 is sent from an analog signal processor 13 and successively processed by an A/D converter 14, a digital signal processor 15, a buffer memory 16, and an image compressor 17. The analog signal processor 13 subjects the image signal outputted from the imaging sensor 11 to gamma processing or other such analog signal processing. The A/D converter 14 converts the analog signal outputted from the analog signal processor 13 into a digital signal. The digital signal processor 15 subjects the image signal converted into a digital signal by the A/D converter 14 to digital signal processing such as noise elimination or contour enhancement. The buffer memory 16 is a RAM (Random Access Memory), and temporarily stores the image signal. The image signal stored in the buffer memory 16 is sent to and processed by first the image compressor 17 and then an image recorder 18. The image signal stored in the buffer memory 16 is read at a command from an image recording controller 19 and sent to the image compressor 17. The data of the image signal sent to the image compressor 17 is compressed into an image signal according to a command from the image recording controller 19. This compression adjusts the image signal to a smaller data size than that of the original data. An example of the method for compressing the image signal is the JPEG (Joint Photographic Experts Group) method in which compression is performed on the image signal for each frame. After this, the compressed image signal is recorded by the image recording controller 19 to the image recorder 18. When a moving picture is recorded, JPEG was used to compress a plurality of image signals, compressing an image signal for each frame, and an H.264/AVC method can also be used, in which compression is performed on image signals for a plurality of frames all at once.

The image recorder 18 produces a still picture file or moving picture file that is associated with specific information to be recorded with the image signal. The image recorder 18 also records the still picture file or moving picture file on the basis of a command from the image recording controller 19. The image recorder 18 is a removable memory and/or an internal memory, for example. The specific information to be recorded with the image signal includes the date the image was captured, focal length information, shutter speed information, aperture value information, and photography mode information. Still picture files are in Exif (TRADEMARK) format or a format similar to Exif (TRADEMARK) format. Moving picture files are in H.264/AVC format or a format similar to H.264/AVC format.

(6) Image Display Unit

The image display unit 36 has the display unit 20 and an image display controller 21. The display unit 20 is a liquid crystal monitor, for example. The display unit 20 displays as a visible image the image signal recorded to the buffer memory 16 or the image recorder 18 on the basis of a command from the image display controller 21. Possible display modes on the display unit 20 include a display mode in which only the image signal is displayed as a visible image, and a display mode in which the image signal and information from the time of capture are displayed as a visible image.

(7) Viewfinder

The viewfinder unit 38 has a liquid crystal viewfinder 8 that displays the image acquired by the imaging sensor 11, and a viewfinder eyepiece window 9 provided to the rear face of the case 3 a. The user looks into the viewfinder eyepiece window 9 to view the image displayed on the liquid crystal viewfinder 8.

(8) Battery

The battery 22 supplies power to the various components of the camera body 3, and also supplies power to the interchangeable lens unit 2 via the lens mount 95. In this embodiment, the battery 22 is a rechargeable battery. The battery 22 may be a dry cell, or may be an external power supply, with which power is supplied from the outside through a power cord.

Tracking Table

With the digital camera 1, electronic tracking is performed by the focus adjusting unit 72 so that the focal length can be varied while the subject distance is kept substantially constant. More specifically, as shown in FIG. 14, to perform electronic tracking, a tracking table 100 is held in the memory 40 a. This tracking table 100 shows the relationship between the rotational position of the zoom ring 84 and the position of the focus lens unit 75 in the Z axis direction with respect to the second lens group unit 77. For example, the memory 40 a holds three tracking tables 100 corresponding to subject distances of 0.3 m, 1.0 m, and infinity (∞). The infinity is an example of a first subject distance.

The tracking table 100 consists of discrete information in which the rotational position of the zoom ring 84 and the position of the focus lens unit 75 in the Z axis direction are divided into several groups. In general, the number of divisions is determined so that the subject distance will fit within a specific subject field depth even if the zoom ring 84 is turned.

The rotational position of the zoom ring 84 (position in the rotational direction) can be detected by the linear position sensor 87. On the basis of this detection result and the tracking table 100, the lens microcomputer 40 can determine the position of the focus lens unit 75 in the Z axis direction with respect to the second lens group unit 77.

The starting point position D of the focus lens unit 75 with respect to the second lens group unit 77 is detected by the photosensor 67, which is indicated by the one-dot chain line in FIG. 14. The focus lens unit 75 is able to move within a range from a position E1 to a position E2, on the basis of all the tracking tables. In this embodiment, the starting point position D is located in the middle of the total movement range E, within the total movement range E of the focus lens unit 75 (between positions E1 and E2). Thus disposing the starting point position D in the middle of the total movement range E allows the focus lens unit 75 to be moved relatively quickly to any position when the power is turned on to the digital camera 1, for example. Consequently, the start-up time for switching the state of the digital camera 1 from a stopped state to an imaging enabled state can be reduced.

As shown in FIG. 14, the starting point position D is disposed within a movement range G (between a position E2 and a position H1; an example of the first tracking range) of the focus lens unit 75 on the basis of the infinity tracking table 100. In general, the user is most likely to capture an image of a subject at the infinity position when turning on the power to the digital camera 1 and capturing an image of the subject, so the start-up time can be shortened by disposing the starting point position D within the movement range G.

The movement range G of the focus lens unit 75 based on the infinity tracking table 100 includes a movement range H from a position H2 (an example of the first position) to a position H1 (an example of the second position). The position H2 is the position of the focus lens unit 75 at which the optical system L can focus on infinity at the wide angle end. When the focus motor 64 is controlled by the lens microcomputer 40 on the basis of the infinity tracking table 100 in a state in which the rotational position of the zoom ring 84 corresponds to the wide angle end, the focus lens unit 75 moves to the position H2. The position H1 is the position where the focus lens unit 75 is farthest away from the imaging sensor 11 when the focus lens unit 75 is driven on the basis of the infinity tracking table 100.

The starting point position D is disposed in the middle of this movement range H. In general, the optical system L is most likely to be at the wide angle end when the user turns on the power to the digital camera 1 to capture an image of a subject, so the start-up time can be further reduced by disposing the starting point position D in the middle of the movement range H.

The tracking table 100 may also be expressed by a polynomial, rather than discrete information divided into several groups. Position information about the first lens group G1, second lens group G2, or fourth lens group G4 in the Z axis direction may also be used instead of the rotational position of the zoom ring 84. The “position of the focus lens unit 75 in the Z axis direction with respect to the second lens group unit 77” can be rephrased as the position of the third lens group G3 in the Z axis direction with respect to the second lens group unit 77, or the position of the third lens group G3 in the Z axis direction with respect to the second lens group G2.

Operation of the Digital Camera

The operation of the digital camera 1 will be described.

(1) Imaging Mode

This digital camera 1 has two imaging modes. More specifically, the digital camera 1 has a viewfinder imaging mode in which the user looks through the viewfinder eyepiece window 9 to view the subject, and a monitor imaging mode in which the user observes the subject on the display unit 20.

With the viewfinder imaging mode, the image display controller 21 drives the liquid crystal viewfinder 8, for example. As a result, an image of the subject (a so-called through-image) acquired by the imaging sensor 11 is displayed on the liquid crystal viewfinder 8.

With the monitor imaging mode, the display unit 20 is driven by the image display controller 21, for example, and a real-time image of the subject is displayed on the display unit 20. Switching between these two imaging modes can be performed with the mode selector button 34.

(2) Zoom Operation

Next, the operation of the interchangeable lens unit 2 when the user performs zooming will be described.

When the user rotates the zoom ring 84, the cam barrel 51 rotates along with the zoom ring 84. When the cam barrel 51 rotates around the optical axis AZ, the first holder 52 is guided by the first cam grooves 51 d of the cam barrel 51, and advances in the Z axis direction. The second holder 55 and the fourth lens group support frame 61 are also guided by the second cam grooves 51 b and the third cam grooves 51 c of the cam barrel 51, and advance in the Z axis direction. Thus, by rotating the zoom ring 84, the state of the interchangeable lens unit 2 can be changed from the wide angle end state shown in FIGS. 5 and 6 to the telephoto end state shown in FIGS. 7 and 8. Consequently, the subject can be imaged at the desired zoom position by adjusting the rotational position of the zoom ring 84.

The second holder 55 is mechanically driven in the Z axis direction by rotating the zoom ring 84 here, but only the focus lens unit 75 is electrically driven and controlled by the focus adjusting unit 72 on the basis of the tracking table 100 stored ahead of time in the memory 40 a, so that the subject distance remains substantially constant. For example, when the focus lens unit 75 is driven by the focus motor 64 on the basis of the tracking table 100, the focal state can be kept at infinity both when the move is from the wide angle end to the telephoto end, and when the move is from the telephoto end to the wide angle end.

More precisely, when the zoom ring 84 is turned, the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 move in the Z axis direction along the optical axis AZ. Consequently, the magnification of the subject image changes. At this point the third lens group G3 also moves in the Z axis direction along the optical axis AZ in a state of being supported by the second holder 55 via the third lens group support frame 56. When there is a relative change in the positional relationship of the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4, the focal state of the subject image formed on the imaging sensor 11 also changes. That is, the subject distance at which the focal point is formed on the imaging sensor 11 changes.

In view of this, with the digital camera 1, even if the focal length changes, the subject distance can be kept substantially constant by driving the focus motor 64 according to the rotational position of the zoom ring 84. More specifically, using just the focus motor 64, the focus lens unit 75 including the third lens group G3 is driven with respect to the second lens group unit 77. The lens microcomputer 40 acquires the rotational position of the zoom ring 84 on the basis of the detection signal of the linear position sensor 87. At the same time, the lens microcomputer 40 calculates the position of the focus lens unit 75 with respect to the second lens group unit 77 from the count value at the counter 40 b. Utilizing the plurality of tracking tables 100 shown in FIG. 14, the lens microcomputer 40 finds the current subject distance from these two pieces of information (the current rotational position of the zoom ring 84, and the position of the focus lens unit 75 with respect to the second lens group unit 77), and selects the tracking table 100 corresponding to the subject distance thus found. Here, we will assume that the tracking table 100 corresponding to infinity was selected.

Next, the lens microcomputer 40 again acquires the rotational position of the zoom ring 84, and finds the rotational speed of the zoom ring 84, that is, the rate of change in the focal length, from the amount of change in the rotational position of the zoom ring 84.

Next, the lens microcomputer 40 predicts the rotational position of the zoom ring 84 after the elapse of a specific time from the current rotational angle of the zoom ring 84 and the rotational speed of the zoom ring 84, and finds as a target position the position of the focus lens unit 75 in the Z axis direction corresponding to the predicted rotational position of the zoom ring 84. After the elapse of a specific time, the lens microcomputer 40 drives the focus motor 64 via the focus drive controller 41 so that the focus lens unit 75 will be located at this target position. Consequently, the focus lens unit 75 is driven so as to follow the movement of the other lens groups, and the subject distance is kept constant.

Thus, in the electronic tracking operation, the lens microcomputer 40 predicts the change in the focal length that will accompany zooming operation, and acquires from the tracking table 100 the target position of the focus lens unit 75 corresponding to the predicted focal length. The focus lens unit 75 is driven to the target position by the focus motor 64 in parallel with the zooming operation of the optical system L. Since this operation is executed at specific time intervals, even if the zoom ring 84 is rotated and the focal length of the optical system L changes, the focus lens unit 75 will move to the Z axis direction position corresponding to the focal length on the basis of the tracking table 100, and the drive of the focus lens unit 75 can conform to the change in the focal length. Consequently, the subject distance can be kept substantially constant regardless of any change in the focal length. The control of these components may be performed by the body microcomputer 10, rather than lens microcomputer 40.

Similarly, when the focused subject distance is short, such as 1 m, for example, the tracking table 100 for which the subject distance is 1 m is selected, and both when the move is from the wide angle end to the telephoto end, and when the move is from the telephoto end to the wide angle end, the focused state at a short distance can be maintained by driving the focus motor 64, and the zooming operation can be carried out smoothly.

In particular, since the focus lens unit 75 and the focus motor 64 move in the Z axis direction integrally with the second lens group unit 77, even if the user turns the zoom ring 84 quickly, the focus lens unit 75 can still be moved integrally with the second lens group unit 77. Therefore, if the subject distance is to be kept substantially constant before and after the zooming operation, the focus motor 64 may move the third lens group G3 by a distance obtained by subtracting the distance that the second lens group G2 is moved by the cam mechanism with respect to the imaging sensor 11 from the distance that the third lens group G3 is to be moved with respect to the imaging sensor 11. This makes it easy to keep up with fast operation of the zoom ring 84 by the user.

Also, in this embodiment, if a zooming operation is performed from the wide angle end to the telephoto end, with the subject distance at infinity, the focus lens unit 75 (more precisely, the third lens group G3, which is a focus lens group) must be moved in the Z axis direction by about 3 mm with respect to the imaging sensor 11. When the focus motor 64 is driven at 800 pps, the amount of drive of the focus lens unit 75 per rotation of the focus motor 64 is 0.6 mm as mentioned above, so it takes 0.25 second to move the focus lens unit 75 by 3 mm in the Z axis direction on the basis of the tracking table. Since it is possible to move the focus lens unit 75 from the wide angle end to the telephoto end in approximately 0.25 second, even if the user should turn the zoom ring 84 from the wide angle end to the telephoto end in 0.5 second, the drive of the focus lens unit 75 can keep up with the change in focal length. Consequently, even if the user should perform a quick zooming operation while looking at the subject on the display unit 20 in live view mode, for example, the subject image that shows on the display unit 20 will be unlikely to be blurred, and this makes the camera easier to use.

(3) Focusing Operation

Next, the focusing operation of the digital camera 1 will be described. The digital camera 1 has two focus modes: an auto-focus imaging mode and a manual imaging mode. The user of the digital camera 1 can select the focus mode with a focus imaging mode setting button (not shown) provided to the camera body 3.

In the auto-focus imaging mode, auto-focus operation is performed by contrast detection method. When auto-focusing is performed by contrast detection method, the body microcomputer 10 asks the lens microcomputer 40 for contrast AF data. This contrast AF data is necessary in auto-focusing by contrast detection method, and includes, for example, the focus drive speed, focus shift amount, image magnification ratio, and information about whether contrast AF is possible.

The body microcomputer 10 monitors whether or not the shutter button 30 has been pressed half way down. If the shutter button 30 has been pressed half way down, the body microcomputer 10 issues an auto-focus commencement command to the lens microcomputer 40. This auto-focus commencement command is to start the auto-focus operation by contrast detection method. Upon receiving this command, the lens microcomputer 40 drives and controls the focus motor 64, which is a focus actuator. More precisely, the lens microcomputer 40 sends a control signal to the focus drive controller 41. On the basis of this control signal, the focus drive controller 41 drives the focus motor 64, and the focus lens unit 75 moves minutely.

The body microcomputer 10 calculates an evaluation value for auto-focus operation (hereinafter referred to as an AF evaluation value) on the basis of the received image data. More specifically, the body microcomputer 10 sends a command to the digital signal processor 15. The digital signal processor 15 sends an image signal to the body microcomputer 10 at a specific timing on the basis of the received command. The body microcomputer 10 finds a brightness signal from the image data produced by the imaging sensor 11, and finds the AF evaluation value by integrating the high-frequency component within the screen of the brightness signal. The AF evaluation value thus calculated is stored in a DRAM (not shown) in a state of being associated with the exposure synchronization signal. Since the lens position information acquired by the body microcomputer 10 from the lens microcomputer 40 is also associated with the exposure synchronization signal, the body microcomputer 10 can store the AF evaluation value with it associated with the lens position information.

Next, the body microcomputer 10 extracts as the focal point the position of the focus lens unit 75 where the AF evaluation value is at its maximum, on the basis of the AF evaluation value stored in the DRAM. The method for driving the focus lens unit 75 in the extraction of the focal point is generally known as a hill climbing method. With a hill climbing method, the focus lens unit 75 is moved in the direction of increasing the AF evaluation value, and the AF evaluation value is found for each position of the focus lens unit 75. This operation is continued until the maximum value for the AF evaluation value is detected, that is, until the AF evaluation value increases up to its peak and the begins to decrease.

The body microcomputer 10 sends a control signal to the focus drive controller 41 via the lens microcomputer 40 so that the focus lens unit 75 will be driven to the position corresponding to the extracted focal point. The focus drive controller 41 produces a drive pulse for driving the focus motor 64 on the basis of a control signal from the body microcomputer 10 (or the lens microcomputer 40), for example. The focus motor 64 is driven by an amount corresponding to this drive signal, and the focus lens unit 75 moves in the Z axis direction to the position corresponding to the focal point.

Focusing in auto-focus imaging mode is performed in this way with the digital camera 1. The above operation is executed instantly when the user presses the shutter button 30 half way down.

Focusing by contrast detection method can also be carried out in monitor imaging mode (known as viewfinder mode), in which real-time image data can be produced with the imaging sensor 11. The reason for this is that in viewfinder mode, image data is produced in a steady state by the imaging sensor 11, and auto-focusing by contrast detection method using this image data is easy.

In viewfinder mode, since a real-time image of the subject is displayed on the display unit 20, the user can decide on the composition for taking the still picture or moving picture while looking at the display unit 20. Also, there is another imaging mode the user can select in addition to live view mode using the display unit 20, which is a second live view mode (viewfinder imaging mode) in which the subject image from the interchangeable lens unit 2 is guided to the liquid crystal viewfinder 8 (viewfinder unit 38).

The manual focus imaging mode will now be described.

When the user turns the focus ring 89, the focus ring angle detector 90 detects the rotational angle of the focus ring 89 and outputs a signal corresponding to this rotational angle. The focus drive controller 41 is able to receive signals from the focus ring angle detector 90, and able to send signals to the focus motor 64. The focus drive controller 41 sends the decision result to the lens microcomputer 40. The focus drive controller 41 drives the focus motor 64 on the basis of a control signal from the lens microcomputer 40. More precisely, the lens microcomputer 40 produces a drive signal for driving the focus motor 64 on the basis of a focus ring rotational angle signal. When the lead screw 64 a of the focus motor 64 rotates according to the drive signal, the focus lens unit 75 moves in the Z axis direction via the rack 66 that meshes with the lead screw 64 a. In the wide angle end state shown in FIGS. 5 and 6, the subject distance is infinity, but as the subject distance draws closer, the focus lens unit 75 moves to the Z axis direction positive side. Similarly, in the telephoto end state shown in FIGS. 7 and 8, the subject distance is infinity, but as the subject distance becomes shorter, the focus lens unit 75 moves to the Z axis direction positive side. The amount of movement of the focus lens unit 75 is greater in this case than in the case of the wide angle end.

In this way, the user can perform focusing by turning the focus ring 89 while looking at the subject on the display unit 20. In the manual focus imaging mode, when the user presses the shutter button 30 all the way down, imaging is performed in this unchanged state.

(4) Still Picture Imaging

When the user presses the shutter button 30 all the way down, a command is sent from the body microcomputer 10 to the lens microcomputer 40 so that the aperture value of the optical system L will be set to the aperture value calculated on the basis of the light measurement output of the imaging sensor 11. The aperture drive controller 42 is controlled by the lens microcomputer 40, and the aperture unit 62 is constricted to the indicated aperture value. Simultaneously with the indication of the aperture value, a drive command is sent from the imaging sensor drive controller 12 to the imaging sensor 11, and a shutter unit 33 drive command is sent out. The imaging sensor 11 is exposed by the shutter unit 33 for a length of time corresponding to the shutter speed calculated on the basis of the light measurement output of the imaging sensor 11.

The body microcomputer 10 executes imaging processing and, when the imaging is completed, sends a command signal to the image recording controller 19. The image recorder 18 records an image signal to an internal memory and/or removable memory on the basis of the command of the image recording controller 19. The image recorder 18 records imaging mode information (whether auto-focus imaging mode or manual focus imaging mode) along with the image signal to the internal memory and/or removable memory on the basis of the command of the image recording controller 19.

Upon completion of the exposure, the imaging sensor drive controller 12 reads image data from the imaging sensor 11, and after specific image processing, image data is outputted via the body microcomputer 10 to the image display controller 21. Consequently, the captured image is displayed on the display unit 20.

Also, upon completion of the exposure, the shutter unit 33 is reset to its initial position by the body microcomputer 10. The body microcomputer 10 issues a command to the lens microcomputer 40 for the aperture drive controller 42 to reset the aperture unit 62 to its open position, and a reset command is sent from the lens microcomputer 40 to the various units. Upon completion of this resetting, the lens microcomputer 40 tells the body microcomputer 10 that resetting is complete. After the resetting completion information has been received from the lens microcomputer 40, and after a series of post-exposure processing has been completed, the body microcomputer 10 confirms that the shutter button 30 is not being pressed, and the imaging sequence is concluded.

(5) Moving Picture Capture

The digital camera 1 also has the function of capturing moving pictures. In moving picture imaging mode, image data is produced by the imaging sensor 11 at a specific period, and the image data thus produced is utilized to continuously carry out auto-focusing by contrast detection method. In moving picture imaging mode, if the shutter button 30 is pressed, or if the moving picture capture operation button 24 is pressed, a moving picture is recorded to the image recorder 18, and when the shutter button 30 or the moving picture capture operation button 24 is pressed again, recording of the moving picture by the image recorder 18 is stopped.

Features of Digital Camera

The features of the digital camera 1 described above are as follows.

(1) With this digital camera 1, the photosensor 67 can detect whether or not the focus lens unit 75 is disposed at the starting point position D with respect to the second lens group unit 77. Furthermore, the starting point position D is disposed within the total movement range E. As a result of this constitution, the drive time it takes to move the focus lens unit 75 from the starting point position D to a specific position within the total movement range E can be shorter. Consequently, the start-up time can be reduced with this digital camera 1.

(2) With this digital camera 1, three tracking tables 100 are used as tracking information, the starting point position D is disposed within the movement range G of the focus lens unit 75 based on the tracking tables 100 with a subject distance of infinity and 1 m, and the starting point position D is not disposed in the movement range of the tracking table 100 with a subject distance of 0.3 m. When there is thus a high probability of use of one of the tracking tables 100, the drive time for moving the focus lens unit 75 from the starting point position D to a specific position can be made shorter by disposing the starting point position D within the movement range of the focus lens unit 75 based on one of the tracking tables 100.

For example, with this digital camera 1, the starting point position D is disposed in the movement range G of the focus lens unit 75 based on the infinity tracking table 100. In general, the user is most likely to capture an image of a subject at the infinity position when turning on the power to the digital camera 1 and capturing an image of the subject, so the start-up time can be shortened by disposing the starting point position D within the movement range G.

(3) With this digital camera 1, since the starting point position D is disposed in the middle of the total movement range E, the drive time can be shortened when moving the focus lens unit 75 to any position within the total movement range E.

(4) With this digital camera 1, the movement range H of the focus lens unit 75 based on the infinity tracking table 100 includes the movement range H from the position H2 corresponding to the wide angle end to the position H1 at which the focus lens unit 75 is farthest away from the imaging sensor 11. The starting point position D is disposed in the middle of this movement range H. In general, the optical system L is most likely to be at the wide angle end when the user turns on the power to the digital camera 1 and captures an image of the subject, so the start-up time can be shortened by disposing the starting point position D in the middle of the movement range H.

Other Embodiments

Embodiments are not limited to those discussed above, and various changes and modifications are possible without departing from the gist of the present invention. Also, the above embodiment are basically just favorable examples, and are not intended to limit the present invention, its applications, or the scope of these applications.

(1) In the above embodiment, the digital camera 1 was capable of capturing both moving and still pictures, but may instead be capable of capturing just still pictures, or just moving pictures.

(2) In the above embodiment, the digital camera 1 may be, for example, a digital still camera, a digital video camera, a mobile telephone equipped with a camera, or a PDA equipped with a camera.

(3) Although the above-mentioned digital camera 1 was not described as including a quick return mirror, it may have a quick return mirror similar to conventional single reflex lens cameras.

(4) The configuration of the optical system L is not limited to that in the above embodiment. For example, the third lens group G3 may be made up of a plurality of lenses, and the second lens group G2 may be made up of just a single lens. Also, the layout of the optical system L is not limited to that shown in FIGS. 12A-12B.

(5) In the above embodiment, the exposure time to the imaging sensor 11 was controlled by operating the shutter unit 33, but the exposure time of the imaging sensor 11 may instead be controlled by an electronic shutter.

(6) In the above embodiment, electronic tracking was performed by the lens microcomputer 40, but a command may be sent from the body microcomputer 10 to the lens microcomputer 40, and the control of the electronic tracking performed on the basis of this command.

(7) In the above embodiment, the starting point position D was disposed in the middle of the movement range H, but as shown in FIG. 15, the starting point position D may be disposed in the middle of the movement range G. Here again, the start-up time can be shortened because the starting point position D is determined using as a reference the tracking table 100 in which the subject distance is infinity.

(8) In the above embodiment, the starting point position D was determined using as a reference the tracking table 100 in which the subject distance was infinity, but another tracking table 100 may be used instead. For example, as shown in FIG. 16, the starting point position D may be determined using as a reference the tracking table 100 in which the subject distance is 0.3 m.

More specifically, as shown in FIG. 16, the starting point position D is disposed within a movement range J (between a position JT and a position J2; an example of the first tracking range) of the focus lens unit 75 based on the tracking table 100 in which the subject distance is 0.3 m. More precisely, the starting point position D is disposed in the middle of the movement range J. The position J2 is the position of the focus lens unit 75 corresponding to the wide angle end. The position JT is the position where the focus lens unit 75 is farthest away from the imaging sensor 11.

For example, if the optical system L is an optical system used for macro imaging, it is most likely that the imaging will take place at the shortest subject distance of 0.3 m, so the start-up time can be shortened by disposing the starting point position D in the middle of the movement range J.

(9) In the above embodiment, the starting point position D was disposed in the middle of the total movement range E, but the starting point position D may be shifted from the middle of the total movement range E to the extent that the start-up time can still be shortened. That is, the starting point position D may be disposed substantially in the middle of the total movement range E.

Also, the starting point position was disposed in the middle of the movement range H, but the starting point position D may be shifted from the middle of the movement range H to the extent that the start-up time can still be shortened. That is, the starting point position D may be disposed substantially in the middle of the movement range H.

Furthermore, the starting point position D may be shifted from the middle of the movement range J to the extent that the start-up time can still be shortened. That is, the starting point position D may be disposed substantially in the middle of the movement range J.

(10) The tracking tables 100 shown in FIGS. 14 to 16 are examples, and the tracking tables are not limited to the tracking tables 100 discussed above. In the above embodiment, although the tracking table in which the subject distance was infinity (∞) is arranged at a closest position to the imaging element in FIGS. 14 to 16 (that is, at a lowest position in FIGS. 14 to 16), the tracking table in which the subject distance is short, such as 0.3 m, may be arranged at a closest position to the imaging element in FIGS. 14 to 16. With such optical system, the effect will be the same as that in the embodiments given above.

While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Thus, the scope of the invention is not limited to the disclosed embodiments. 

1. A lens barrel for forming an optical image of a subject on an imaging element, comprising: a first lens unit having a first lens element and a first lens support frame supporting the first lens element; a second lens unit having a second lens element arranged to vary the focal length by moving relative to the first lens element in the optical axis direction, and a second lens support frame supporting the second lens element; a focus lens unit having a focus lens arranged to vary the focal state of the optical image by moving relative to the first lens element or the second lens element in the optical axis direction, and a focus lens support frame supporting the focus lens; a zoom mechanism arranged to relatively move the first lens unit and the second lens unit in the optical axis direction, having a zoom operating unit arranged to be operated by the user, with which the operating force inputted to the zoom operating unit is mechanically transmitted to at least one of the first lens unit and the second lens unit; a focus actuator supported by the zoom mechanism to move integrally with the first lens unit, and configured to utilize electric power to drive the focus lens unit in the optical axis direction with respect to the first lens unit; a starting point detector configured to detect whether or not the focus lens unit is disposed at a starting point position with respect to the first lens unit; and a drive controller configured to control the focus actuator so that the focus lens unit moves within a tracking range including the starting point position.
 2. The lens barrel according to claim 1, wherein the drive controller is configured to control the focus actuator on the basis of preset tracking information, the tracking information comprises a first tracking table with which the focus actuator can be controlled so that the in-focus object distance is kept substantially at a first subject distance even if the focal length changes, and a second tracking table with which the focus actuator can be controlled so that the in-focus object distance is kept substantially at a second subject distance even if the focal length changes, when the focus actuator is controlled by the drive controller on the basis of the first tracking table, the focus lens unit is arranged to move in the optical axis direction within a first tracking range, and the starting point position is disposed within the first tracking range, which is at least part of the tracking range.
 3. The lens barrel according to claim 1, wherein the starting point position is disposed substantially in the middle of the tracking range in the optical axis direction.
 4. The lens barrel according to claim 2, wherein the starting point position is disposed substantially in the middle of the first tracking range in the optical axis direction.
 5. The lens barrel according to claim 2, wherein the first subject distance of the first tracking table is infinity.
 6. The lens barrel according to claim 5, wherein the first tracking range is a range from a first position, at which the focal point can be infinity in a state in which the focal length is the wide angle end, to a second position, at which the focus lens unit is farthest away from the imaging element when the focus lens unit is driven on the basis of the first tracking table.
 7. The lens barrel according to claim 2, wherein the first subject distance of the first tracking table is shorter than the second subject distance.
 8. The lens barrel according to claim 2, wherein the first subject distance of the first tracking table is the shortest of all the subject distances in the tracking tables included in the tracking information.
 9. An imaging device, comprising: the lens barrel according to claim 1; and a camera body having the imaging element.
 10. The lens barrel according to claim 2, wherein the starting point position is disposed substantially in the middle of the tracking range in the optical axis direction.
 11. A lens barrel for forming an optical image of a subject on an imaging element, comprising: a linear position sensor detecting a rotational position of a zoom ring which moves one of a first lens unit and a second lens unit in an optical axis direction to vary a focal length; a focus lens unit position sensor detecting a position of a focus lens unit, the focus lens unit having a focus lens arranged to vary the focal state of the optical image by moving relative to a first lens element of the first lens unit or a second lens element of the second lens unit in the optical axis direction; a focus actuator configured to utilize electric power to drive the focus lens unit in the optical axis direction with respect to the first lens unit; a controller coupled to the focus actuator, the linear position sensor, and the focus lens unit position sensor; a first memory portion including a tracking table defining a relationship between a position of the focus lens and the rotational position of the zoom ring; and a second memory portion coupled to the controller, the second memory portion including instructions for configuring the controller to control the focus actuator so that the position of the focus lens unit conforms to changes in the focal length in accordance with the tracking table.
 12. The lens barrel according to claim 11, wherein the tracking table contains information indicating the positions of the focus lens unit at which a focused subject distance remains substantially constant when the focal length changes.
 13. The lens barrel according to claim 11, wherein the tracking table contains information indicating the positions of the focus lens unit at which the focused subject distance remains substantially constant when the focal length changes for specific subject distance categories.
 14. The lens barrel according to claim 11, wherein the controller is configured to control the focus actuator so that a starting position of the focus lens unit is substantially in a midpoint of a range of positions of the focus lens unit in the tracking table. 